Indian Journal of Genetics and Plant Breeding (The)

A collection of 40 self-compatible types of Brassica campestris var. brown sarson, representing a broad spectrum of the diversity in this group in the Indo-Gangetic belt, was examined over two years for genetic divergence among these populations. Six characters related to fitness, namely days to first flower, number of primary branches, number of secondary branches, height, number of siliquae on main axis and seeds per siliqua were studied.

The study revealed considerable variability among the self-compatible types for all the characters except for the number of primary branches.

On the basis of multivariate analysis using Mahalanobis D²-statistic to measure the divergence, the forty populations could be grouped into nine clusters. The divergence between the populations could not be related to their geographical distribution.

Among the characters which contributed maximum to divergence were, height, seeds per siliqua and primary branches in order of merit, while secondary branches contributed the least to divergence. Inter and intra-cluster divergence revealed the operation of parallel forces of differentiation at both the levels.

The causes for divergence in self-compatible types appeared to be their mixed cropping pattern, frequent floods in the areas of their cultivation, extremely variable environments within the same season, consumer preference and genetic drift under inbreeding. The restricted distribution of self-compatible types was discussed in relation to their limited capacity to stand wide agro-climatic conditions unlike the widely adapted incompatible brown sarson.